In a stringed musical instrument, such as a guitar, the strings, placed under tension, extend unsupported between a first critical point usually formed by the nut positioned where the neck joins the head and a second critical point usually formed by a clearly defined point on the bridge positioned on the body. The strings are secured or fixed at one end on the body of the instrument to what is traditionally known as the tailpiece, strung over the bridge and extended past the nut at the transition from the neck instrument to the head, and, for conventional instruments, secured at the other end to the tuning pegs where an untensioned string is tensioned and adjusted to a tuned pitched condition, proper playing pitch for play, or, simply, tuned condition; sometimes a nut arrangement is provided for a headless or tuning peg-less design. The neck further comprises a fingerboard or fret board that a player presses the strings against to play various pitches up and down the neck; the fingerboard typically is formed with a convex radius that commonly varies between 9 and 16 inches.
The second critical point can be created as a part of a bridge or combined bridge and tailpiece structure. Traditionally, the size of the bridge element is quite small so as to create a clearly defined single point of contact between the string and the bridge element. It is between these two points that the playable string length is typically determined, sometimes referred to as the scale length or harmonic length. Adjusting the relative distance between the first and second critical points is called harmonic tuning or setting the intonation. Some bridges structures are individually adjustable, that is for each string, relative to the nut for achieving a more precise harmonic tuning. Usually this adjustment of the second critical point for harmonic tuning is carried out first and then the strings of the instrument are tuned to playing pitch. Often referred to the “initial setup”, it is not uncommon that further adjustment of the harmonic tuning is necessary for a variety of reasons, for example, including changing the brand of a string where the alloy of the strings is varied or when the gauge of strings the player chooses changes as well as “setting” the string by manually pulling on the string along the scale length in order to improve elasticity in the string at first tensioning before the string can confidently relied on to hold proper playing pitch during the life of the string.
Often the typical construction of the strings, particularly for guitar and bass, includes a plain end and, on the other end, a “ball end” which being a washer-like addition is wrapped by the string itself into a larger form to enable “fixing” or securing the string on the instrument to the tailpiece element; alternatives to the “ball end” include as known to those of ordinary skill in the art as “bullet ends” formed from metal and molded around the end of the string. The tailpiece is usually provides for an opening or recess sufficient in size to receive the strings of various diameters ranging from .007″ to .070″ or more while being smaller than the diameter of the ball end so as to limit the passing of the ball end through the opening or recess in order to secure or mount each of the individual strings to the body. The wrapping usually extends up to a ½″ towards the plain end and as such the position of the tailpiece structure relative to the bridge element must insure that the wrapping does not extend over the second critical point when arranged on the instrument; this wrapping, under normal circumstances, is not subject to stretch compared to the rest of the string. In the relevant art, “anchoring” strings is often referred to as attaching or securing a string and understood with the limitation that the anchoring is sufficient so that the string is fixedly attached or secured to the instrument under the typical tensioned conditions of the string that typically range from 16 to 20 lbs or greater. Stable fine adjustments of these and other elements have been a longstanding problem for stringed musical instruments.
Playing pitch or proper playing pitch or pitched string condition is generally understood by one of ordinary skill in the art to be the proper pitch of a guitar string relative to the remaining guitar strings when a guitar is played “in tune.” For example, in a standard tuning arrangement, for a six string guitar, based on the standard A=440 Hz, the playing pitch of the 1st string (highest) is tuned to note E (329.63 Hz), the playing pitch of the 2nd string is tuned to note B (294.94 Hz), the playing pitch of the 3rd string is tuned to note G (196.00 Hz), the playing pitch of the 4th string is tuned to note d (146.83 Hz), the playing pitch of the 5th string is tuned to note A (110 Hz), and the playing pitch of the 6th string is tuned to note E (82.41 Hz).
In the Proelsdorfer U.S. Pat. No. 2,304,597, string tensioning devices placed on the tailpiece for fine tuning the pitch of the strings of violins, guitars and the like, were disclosed; such pitch adjustment is quite limited in range, comprising generally an interval falling between that of a whole tone and a major third at best, and designed to offer the tuning of the strings a minor adjustment of pitch after the general tuning is achieved with the tuning pegs on the head of the instrument which traditionally first provides for raising and adjusting the tension of the strings to pitch from an untensioned condition and then setting the string. This is regarded as fine tuning and the apparatus for doing so, the “fine tuners”, usually comprise an adjustment knob or thumb screw.
It is known to those skilled in stringed musical instrument design and construction that various tremolos have been proposed and utilized for varying the tension of all the strings simultaneously for the purpose of creating a tremolo sound. Further, it is known to those skilled in the art that there are a great many commonly used names for such devices, such as tremolo, tremolo device, tremolo tailpiece, tremolo bridge, fulcrum tremolo, fulcrum tremolo bridge, fulcrum tremolo tailpiece, fulcrum tremolo bridge-tailpiece, vibrato, vibrato bridge, vibrato tailpiece, vibrato bridge tailpiece, etc.
In one specific species, known as the fulcrum tremolo, first introduced in Fender U.S. Pat. No. 2,741,146, shows and provides a device comprising a novel structure, which incorporates the bridge and the tailpiece. The portion supporting the bridge elements is called the bridge plate or the base plate. Further, both the bridge and the tailpiece elements connected to the base plate both move together as the fulcrum tremolo device is pivoted. Accordingly, a singular and defining aspect of the fulcrum tremolo is that the harmonic tuning is upset as the device is pivoted; and, accordingly, for an instrument equipped with a fulcrum tremolo, it is unique in that only restoring all of the strings to a proper pitched condition also simultaneously restores the harmonic tuning for all the strings. The base plate upon which the individual bridge elements are adjustably secured has a beveled ridge portion which is secured to the instrument body by six screws permitting pivotal movement about a fulcrum axis which varies the tension on the strings and produces the desired “tremolo effect”; in general, this device allowed for extensive dropping down of the pitch of all the strings and a modest upward capacity that further enabled the familiar mild pedal steel or Hawaiian guitar vibrato effect provided in gentle pivoting.
In this first vintage fulcrum tremolo, herein referred to as Type I, the metal bridge elements of '146 are loosely held in place by a spring loaded attachment screw arrangement pivotally secured through openings in a small folded portion of the base plate farthest from the fulcrum axis. The bridge elements also incorporate set screws for varying the relative height of the bridge elements and, therefore, height of the respective second critical points relative to the base plate and by extension, to the body and neck.
Typically, in order to facilitate the fulcrum tremolo pivoting about its fulcrum axis, counter springs, as a biasing element, are utilized to counteract or counter balance the pull of the strings. Counter springs are usually connected to the body of the instrument at one end and, on the other end, to a separate spring attachment means transverse the base plate, usually a block of metal, milled or cast or a combination of the two, which being secured to the bottom of the base plate by three screws 90 degrees to the base plate, is often called a spring block or inertia block. Upward pitch changes initiated by the use of the fulcrum tremolo in one direction can significantly increase the tension of individual strings.
One of the most troublesome problems with prior art for the fulcrum tremolo has been maintaining the “initial position” achieved at “initial setup” when all the strings are brought to proper playing pitch as the harmonic tuning is achieved. When a musician plays on the string there is usually some kind of string stretch over time that results in the overall tuning, and thereby, the “initial position” going out of balance. Specifically, when the pitch of the string changes, the position of the fulcrum tremolo and the position of the second critical point relative to the nut changes which then instantly alters the harmonic tuning.
This singular characteristic adds complexities in obtaining the primary goal of achieving a stable equilibrium between the force of the tension provided by the two to five biasing or counter springs (connected between the tremolo and the body) in relation to force of tension of all the strings (connected to the fulcrum tremolo and the end of the neck at the peg head by the tuning pegs or an optional nut arrangement that secures the strings without tuning pegs, etc.)
Accordingly, these and other inherences need to be addressed in achieving a true and lasting initial position for the fulcrum tremolo and has been the object of many inventions. In this inherent inter-dependant system of tensioning forces, contrary to the requirements of other tremolo or fixed bridge arrangements, (in the ideal instance where the essential conditions of the initial setup have been established and the appropriate tensioning force of the springs provisioned), the precise tensioning to proper playing pitch for any less than the total number of strings will inherently fail to achieve pitch and harmonic tuning for all of those strings attached to the tremolo.
Initial position refers to the position of the fulcrum tremolo and, therefore, the position of the second critical point on the bridge elements in relation to the first critical point on the nut such that the tension of the strings, each at the intended proper pitched condition, and the appropriately tensioned counter springs, renders a specific equilibrium point wherein the harmonic tuning for all the strings is simultaneously achieved. Often the pivot means is subject to wear and the tremolo does not always return to its initial position. Great care is required to establish the initial position since both aspects of adjustment are interactive and it simultaneously provides both the proper harmonic tuning and proper pitch tuning for each of the individual strings in order to enable a lasting “initial setup”.
Improvements to the Fender '146 fulcrum tremolo have included using string clamps at the nut and at a point on the opposite side of the intonation point or second critical point on each of the bridge elements relative to the nut in order to limit string stretch to the prime vibratory portion of the string within these two points defining the scale length.
Therefore, for stringed musical instruments, as is known to those skilled in the art:                The second critical point is a clearly defined point on the bridge or individual bridge elements, the adjustment of which relative to the first critical point on the nut defines the length of the string or scale length and the adjustment of which is called harmonic tuning.        
For fulcrum tremolos as originated by Fender U.S. Pat. No. 2,741,146, when pivoted:                Both the bridge portions and the string anchoring means, the tailpiece, simultaneously move about a common fulcrum axis;        The harmonic tuning is upset and is only restored when all strings are at proper playing pitch;        The tuning pegs or other means of tensioning the strings are inter-dependant with each other in obtaining initial position; and        Various factors can disturb the equilibrium point between the tension of the strings and the tension of the counter springs and as a consequence disturb the initial position.        
For those fulcrum tremolos equipped with fine tuners as with Rose U.S. Pat. No. 4,497,236, Storey U.S. Pat. No. 4,472,750 and Fender U.S. Pat. No. 4,724,737:                The bridge and tailpiece portions simultaneously move about the fulcrum axis when the device is pivoted for the tremolo effect;        The fine tuner screws simultaneously move with the bridge and tailpiece portions about the tuning axis when fine tuning; and        Fine tuners are designed to offer the tuning of the strings a minor adjustment of pitch after the general tuning is first achieved, typically, by the tuning pegs on the head of the instrument; and        Adjusting the tension of a string by the fine tuner knob alone simultaneously adjusts the harmonic and pitch tuning and can achieve tuning a string to proper pitch conditions while simultaneously achieving proper harmonic tuning.        
Knife Edge Pivots for the Fulcrum Tremolo Rose (U.S. Pat. No. 4,171,661) shows adopting a novel shaped beveled edge to the base plate, called a “knife edge”, adjustably supported by two screw-like members, referred to generally as riser posts, positioned in the body to collectively improve the return to initial position after pivoting the fulcrum tremolo device. The knife edge fulcrum pivot arrangement provides for the base plate to be positioned generally parallel to the instrument body, often referred to as a floating tremolo, for example, and offered the novel possibility to substantively increase the tension of the string for upward pitch changes. Later iterations of Fender '146, herein referred to as Type I, included, similar to Rose, a knife-edge design on the leading edge, closest to the nut, of the base plate with a riser post arrangement adjustably connected to the fulcrum tremolo, herein referred to as Type II.
These two vintage fulcrum tremolos of the last century, Fender in the 50's and Rose in the 80's, are in part distinguished by the differing standards for the placement of the riser posts, that receive each of the knife-edges to create a pivot axis, relative to both first critical point on the nut as well as the second critical point on the bridge element.
Further, for the knife-edge fulcrum design of Type I and Type II, the axis, created at the contact point between each of the two knife-edges and their respective riser posts formed to receive them, is offset from the centerline of the riser post by approximately .090″, and are said to be in close proximity to each other, in view of the dimensions of circular indent design on the riser post that receives the knife-edge provision. “Close Proximity” means a dimension approximately half the diameter of either the riser post element or bearing axle element, which ever is larger, typically less that .125″. Since the individual parts of the two vintage designs were generally not compatible, those who had guitars with the Type II spacing were limited to tremolos that had fine tuner arrangements and string locks while those guitars with the Type I spacing were limited to those tremolos without fine-tuners and string locks.
Another unique feature of the knife-edge based fulcrum tremolo is that the unit is secured entirely by the tension of the counter springs within the body on the one hand and the strings themselves over the top of the body. The combined forces pull the tremolo towards the head or nut of the instrument so that each of the two semi-circular knife edge portions in the base plate pivot against a V-shaped annular recess in each respective riser post. Given the asymmetrical position of strings and springs, and unequal distance between the fulcrum axis to the second critical point relative to the distance from the fulcrum axis to the end of the inertia or spring block, there is a tendency for the tremolo to “lift” away from the body. The annular recess comprises a specific shape to ensure the knife-edge portions of the base plate do not dislocate from the riser posts in initial position or during pivoting.
Bearing Improvements
Further improvements in the fulcrum tremolo in the 90's and into the new millennium utilize various novel arrangements for pivotally supporting the fulcrum tremolo so that the base plate can be variably spaced from the surface of the body. Using bearing devices that include riser posts and at least a portion of the surface of a ball bearing or the like at the pivot point adjustably mounted to the body could encompass a range of bearing devices including self-aligning bearing arrangements affording a universal joint type movement to typical ball bearings and, as such, the bearing arrangements, thereby, not only provided greater adjustment for installations but substantially improved return to initial position after use of the tremolo while virtually eliminated the wear and tear associated with knife-edge and other related prior art (McCabe U.S. Pat. No. 5,965,831 (“'831”), U.S. Pat. No. 5,986,191 (“'191”), U.S. Pat. No. 6,175,066 (“'066”), U.S. Pat. No. 6,563,034 (“'034”), U.S. Pat. No. 6,891,094 (“'094) and U.S. Pat. No. 7,470,841 (”'841)).
The preferred bearing arrangement of '066, '831 and '094 which share the same parent application showed bearing devices supported on pins or shafts positioned between each of two fork-like portions formed in the base plate. The bearing devices are positioned within a bearing housing that received threaded riser posts for adjustably securing the fulcrum tremolo to the instrument body. The preferred bearing arrangement of '191 and '841 showed bearing devices supported on pins or shafts extending outwardly, each from the sides of the base plate, and positioned within a bearing housing that received threaded riser posts for adjustably securing the fulcrum tremolo. A preferred bearing arrangement of '034 and '841 showed bearing devices supported on a single bearing axle or shaft located at the leading edge of the base plate closest the nut within a tube-like housing connected to housings for receiving the bearing devices. One of the two bearing arrangements of '191 and '841 require non-standardized placement of the riser posts that create the position of the pivot axis in view of Type I and II whereas another design, as was the case of '034 bearing arrangements, did not.
Other improvements to bearing arrangements for fulcrum tremolos found expression in Hirayama U.S. Pat. No. 6,710,235 showing an electric guitar having a first critical point on the neck or nut and a second critical point defined to be on the tremolo base plate further pivotally secured to a body. In this patent the bearing arrangement includes a “hinge mechanism” for “supporting the base plate such that the base plate pivots relative to the body”. Bracket pins create the pivot axis. Misalignments of the bracket pins can cause binding in the bearings and defeat the primary goal of successfully returning the fulcrum tremolo to the initial position.
Further, prior collaborative efforts with Gary Kahler and the applicant, Geoffrey McCabe, US Patent No.: U.S. Pat. No. 8,536,431 B1, (“'431”), for example, provide an improvement to the bearing arrangement with an integrated riser post, provided by, in one instance, physically integrating or physically combining the bearing axle housing with the riser posts such that threading the riser posts into inserts in the body secures the bearing axle, the bearing axle housing, the bearing element and the fulcrum tremolo and aligns the centerline of the bearing axle to an abstract plane extending between and including the centerline of the riser post. A bearing axle, formed with an enlarged plain end having a larger diameter greater than the rest of the bearing axle and a second threaded end, extends between and through a first integrated riser post formed for receiving the enlarged plain end and a second integrated riser post that has a threaded opening for receiving the threaded second end. Since the bearing axels pass through the integrated riser posts, they must be rotated in 180 degree increments to adjust height; in some cases, this requirement can lead to installation issues where such precision is inadequate in general or, more particularly, when the instrument has a “set” neck or glued to the body which otherwise precludes the use of neck shims.
In McCabe U.S. application Ser. No. 13/402,825, (“'825”), riser post improvements for inter-cooperation with the bearing axle were introduced in '431 that added greater flexibility of installation and setup to overcome installation limitations inherent in the '431, however, the design requires an increase in part count to yield complete flexibility in adjustment and installation.
Since the axis of the fulcrum tremolo is positioned at an unequal distance from the second critical point relative to the distance to the end of the inertia or spring block, which receives the biasing or counter springs, there is a tendency for the tremolo to “lift” away from the body. Whereas, the knife-edge fitment to the circular indent on the riser post prevented the tremolo from lifting, the issue was addressed in bearing arrangements in alternative ways that often required an additional screws or similar retaining measures, further adding to the complexity and parts count.
There are no existing designs for bearings arrangements, which create the pivot axis, that both allow the conventional placements of the riser posts, as seen in Type I and Type II, and the approximate .090″ offset to create the original feel offered by the traditional proportions. Further, for each of these examples for improved bearing arrangements, the riser posts and bearing housings in all their iterations are marked by reflected and/or non-matching left and right parts used to support the bass side and treble sides of the tremolo, ie, the side that receives the higher pitched strings and those that receive the lower pitched strings. Further, there are no instances where the intersection of the bearing axle and the riser posts are configured to eliminate retaining measures.
Whereas, the knife-edge fitment to the specific circular indent or annular recess on the riser post prevented the tremolo from lifting, the issue was addressed in bearing arrangements in alternative ways that often required additional screws or similar retaining measures, further adding to the complexity and parts count.
Like the many improvements listed above, the installation of the tremolo with ball bearing arrangements by threading the riser post into the instrument can be cumbersome and lengthy since in many cases the riser post elements in the assembly are first combined with the tremolo prior to installation which then requires the riser post on one side of the tremolo be threaded slowly for a short distance and then the riser post on the other side be threaded a short amount until the initial position is finally achieved.